Official Jenkins Docker image

Usage

docker run -p 8080:8080 -p 50000:50000 jenkins/jenkins:lts

NOTE: read below the build executors part for the role of the 50000 port mapping.

This will store the workspace in /var/jenkins_home. All Jenkins data lives in there - including plugins and configuration.
You will probably want to make that an explicit volume so you can manage it and attach to another container for upgrades :

this will automatically create a 'jenkins_home' docker volume on the host machine, that will survive the container stop/restart/deletion.

NOTE: Avoid using a bind mount from a folder on the host machine into /var/jenkins_home, as this might result in file permission issues (the user used inside the container might not have rights to the folder on the host machine). If you really need to bind mount jenkins_home, ensure that the directory on the host is accessible by the jenkins user inside the container (jenkins user - uid 1000) or use -u some_other_user parameter with docker run.

this will run Jenkins in detached mode with port forwarding and volume added. You can access logs with command 'docker logs CONTAINER_ID' in order to check first login token. ID of container will be returned from output of command above.

Backing up data

If you bind mount in a volume - you can simply back up that directory
(which is jenkins_home) at any time.

This is highly recommended. Treat the jenkins_home directory as you would a database - in Docker you would generally put a database on a volume.

If your volume is inside a container - you can use docker cp $ID:/var/jenkins_home command to extract the data, or other options to find where the volume data is.
Note that some symlinks on some OSes may be converted to copies (this can confuse jenkins with lastStableBuild links etc)

Setting the number of executors

You can specify and set the number of executors of your Jenkins master instance using a groovy script. By default its set to 2 executors, but you can extend the image and change it to your desired number of executors :

Configuring reverse proxy

If you want to install Jenkins behind a reverse proxy with prefix, example: mysite.com/jenkins, you need to add environment variable JENKINS_OPTS="--prefix=/jenkins" and then follow the below procedures to configure your reverse proxy, which will depend if you have Apache or Nginx:

Passing Jenkins launcher parameters

Argument you pass to docker running the jenkins image are passed to jenkins launcher, so you can run for sample :

docker run jenkins/jenkins:lts --version

This will dump Jenkins version, just like when you run jenkins as an executable war.

You also can define jenkins arguments as JENKINS_OPTS. This is usefull to define a set of arguments to pass to jenkins launcher as you
define a derived jenkins image based on the official one with some customized settings. The following sample Dockerfile uses this option
to force use of HTTPS with a certificate included in the image

In such a derived image, you can customize your jenkins instance with hook scripts or additional plugins.
For this purpose, use /usr/share/jenkins/ref as a place to define the default JENKINS_HOME content you
wish the target installation to look like :

Preinstalling plugins

You can rely on the install-plugins.sh script to pass a set of plugins to download with their dependencies.
This script will perform downloads from update centers, and internet access is required for the default update centers.

Setting update centers

During the download, the script will use update centers defined by the following environment variables:

❗️ Note that changing this variables will not change the Update Center being used by Jenkins runtime.

Plugin version format

Use plugin artifact ID, without -plugin extension, and append the version if needed separated by :.
Dependencies that are already included in the Jenkins war will only be downloaded if their required version is newer than the one included.

There are also custom version specifiers:

latest - download the latest version from the main update center.
For Jenkins LTS images
(example: git:latest)

experimental - download the latest version from the experimental update center defined by the JENKINS_UC_EXPERIMENTAL environment variable (example: filesystem_scm:experimental)

When jenkins container starts, it will check JENKINS_HOME has this reference content, and copy them
there if required. It will not override such files, so if you upgraded some plugins from UI they won't
be reverted on next start.

In case you do want to override, append '.override' to the name of the reference file. E.g. a file named
/usr/share/jenkins/ref/config.xml.override will overwrite an existing config.xml file in JENKINS_HOME.

to indicate that this Jenkins installation is fully configured.
Otherwise a banner will appear prompting the user to install additional plugins,
which may be inappropriate.

Upgrading

All the data needed is in the /var/jenkins_home directory - so depending on how you manage that - depends on how you upgrade. Generally - you can copy it out - and then "docker pull" the image again - and you will have the latest LTS - you can then start up with -v pointing to that data (/var/jenkins_home) and everything will be as you left it.

As always - please ensure that you know how to drive docker - especially volume handling!

Upgrading plugins

By default, plugins will be upgraded if they haven't been upgraded manually and if the version from the docker image is newer than the version in the container. Versions installed by the docker image are tracked through a marker file.

The default behaviour when upgrading from a docker image that didn't write marker files is to leave existing plugins in place. If you want to upgrade existing plugins without marker you may run the docker image with -e TRY_UPGRADE_IF_NO_MARKER=true. Then plugins will be upgraded if the version provided by the docker image is newer.

Debugging

In order to debug the master, use the -e DEBUG=true -p 5005:5005 when starting the container.
Jenkins will be suspended on the startup in such case,
and then it will be possible to attach a debugger from IDE to it.